The present invention relates to a joining structure of a turbine. More particularly, the present invention relates to a joining structure of a turbine that joins a shaft of a ceramic turbine rotor to a metal shaft.
Generally, in the joining structure of a turbine a shaft of a ceramic turbine rotor and a metal shaft are in abutting connection with each other such that the ceramic turbine rotor and the metal shaft are placed in the same axis. The joined rotor shaft and the metal shaft are enclosed by a sleeve for reinforcement.
One such joining structure is illustrated in FIG. 6A. In a turbine P1, a rotor shaft P3 of a ceramic turbine rotor P2, a sleeve P4 made of a low expansion rate metal are joined to each other by brazing or shrinkage fitting. After the brazing or shrinkage fitting, a metal shaft P6 is welded to an abutment face P5 of the sleeve P4.
In the related-art turbine P7 of FIG. 6B, on the other hand, a rotor shaft P9 of a ceramic turbine P8, a sleeve P10 made of a low expansion rate metal, and a metal shaft P11 are joined into one piece via a joining layer P12 by brazing.
The above joining methods have been found to be insufficient for the following reasons. In the first joining structure, the turbine rotor P2, the sleeve P4, and the metal shaft P6 cannot be joined at the same time, hence requiring additional manufacturing steps. In the second method, if the joint of the sleeve P10 and the metal shaft P11 is heated above 400.degree. C., a brazing material P13 may be oxidized. This reduces the bonding strength and eventually causes disconnection of the metal shaft P11 or damage to the sleeve P10 and the metal shaft P11.
Therefore, an object of the present invention made to overcome the above problems is to provide a joining structure of a turbine which requires fewer manufacturing steps than the conventional structures and which has a high bonding strength.
Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.